Chicken interferon (IFN) is a valuable protein useful in protecting and treating chickens and other fowl from avian viral diseases. Induction of interferon by virus has been successful in primary chick embryo cells "aged" in vitro, with yields ranging from 300 to more than 8,000 units of interferon per 10.sup.7 cells (Marcus, Sekellick and Nichol, Journal of Interferon Research 12:297-305 (1992)).
In addition it is possible that some important parasitic diseases of chickens like that caused by Eimeria may be controllable by interferon through its effects on the immune system. Interferon is gaining increased attention as an antiparasitic agent, (Murray, Journal Interferon Research, 12:319-322 (1992)).
Many factors determine how much interferon is induced by a particular virus. These factors include its origin and passage history, the host cell, incubation conditions and time, and the multiplicity of infection. Stewart, "The Interferon System", 2nd. ed., Vienna:Springer-Verlag, pp 27-57; Marcus, Sekellick and Nichol, Journal of Interferon Research, 12:297-305 (1992).